feat: add hallmark design skill

Anti-AI-slop design skill (greenfield pages, audits, redesigns, design
extraction from URLs/screenshots) -- installed and validated in an
earlier session, was sitting untracked. Full reference library:
components, macrostructures, themes, genres, verbs (audit/redesign).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

skills/hallmark/references/components/f4-step-sequence.md

@@ -0,0 +1,11 @@
+### F4 · Step sequence
+Numbered stages (`1.0 → 2.0 → 3.0`) flow vertically. Each stage has a heading, a paragraph, sometimes a small visual.
+*Use when:* the product is a workflow, not a single moment.
+*Don't confuse with:* F2 Sticky-scroll (which doesn't number stages).
+
+```html
+<ol class="steps">
+  <li><span class="stage">1.0</span><h3>Intake.</h3><p>…</p></li>
+  <li><span class="stage">2.0</span><h3>Plan.</h3><p>…</p></li>
+</ol>
+```